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Modeling and optimization of a regional waste-to-energy system: a case study in central Sweden
Mälardalen University, School of Sustainable Development of Society and Technology. (bioenergy group)
2011 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Conversion of wastes to energy by different technologies can contribute greatly to treating waste sustainably, reducing dependency on imported fossil fuels and protecting environment. A static model of energy balance for a certain region is constructed to simulate and optimize the energy system with the purpose to minimize the total costs, including collection, transportation and conversion or treatment of wastes, distribution of energy products as well as import and export of wastes and energy products. The objective is to find optimum positions for building new energy plants and planting energy crops for two scenarios. How to achieve a regional fossil-fuel-free energy system is also analyzed through a case study of the County of Västmanland in central Sweden. The boundary conditions are assumed to be the limit of local waste generation, capacity of energy plants, and the demands of energy products.

Place, publisher, year, edition, pages
2011.
Keyword [en]
waste, sustainable energy system, fossil-fuel-free, optimization
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-13190OAI: oai:DiVA.org:mdh-13190DiVA: diva2:451943
Conference
Proceedings Sardinia 2011, Thirteenth International Waste Management and Landfill Symposium. S. Margherita di Pula, Cagliari, Italy; 3 - 7 October 2011
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2012-11-15Bibliographically approved
In thesis
1. Retrofitting CHP Plant and Optimization of Regional Energy System
Open this publication in new window or tab >>Retrofitting CHP Plant and Optimization of Regional Energy System
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The use of biomass-based combined heat and power (CHP) plants is considered by the EU administration to be an effective way to increase the use of renewables in the energy system, to reduce greenhouse gas emissions and to alleviate the dependency on imported fossil fuels. At present in Sweden, most of the CHP plants are operated in part-load mode because of variations in heat demand. Further use of the potential heat capacity from CHP plants is an opportunity for integration with other heat-demanding processes. Retrofitting the conventional CHP plants by integration with bioethanol and pellet production processes is considered a feasible and efficient way to improve the plants’ performances.

 

Modeling and simulation of the CHP plant integrated with feedstock upgrading, bioethanol production and pellet production is performed to analyze the technical and economic feasibility. When integrating with bioethanol production, the exhaust flue gas from the CHP plant is used to dry the hydrolysis solid residues (HSR) instead of direct condensation in the flue gas condenser (FGC). This drying process not only increases the overall energy efficiency (OEE) of the CHP plant but also increases the power output relative to the system using only a FGC. Furthermore, if steam is extracted from the turbine of the CHP plant and if it is used to dry the HSR together with the exhaust flue gas, pellets can be produced and the bioethanol production costs can be reduced by 30% compared with ethanol cogeneration plants.

 

Three optional pellet production processes integrated with an existing biomass-based CHP plant using different raw materials are studied to determine their annual performance. The option of pellet production integrated with the existing CHP plant using exhaust flue gas and superheated steam for drying allows for a low specific pellet production cost, short payback time and significant CO2 reduction. A common advantage of the three options is a dramatic increase in the total annual power production and a significant CO2 reduction, in spite of a decrease in power efficiency.

 

The retrofitted biomass-based CHP plants play a crucial role in the present and future regional energy system. The total costs are minimized for the studied energy system by using wastes as energy sources. Analyses of scenarios for the coming decades are performed to describe how to achieve a regional fossil fuel-free energy system. It is possible to achieve the target by upgrading and retrofitting the present energy plants and constructing new ones. The conditions and obstacles have also been presented and discussed through optimizing the locations for proposed new energy plants and planting energy crops.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2011
Series
Mälardalen University Press Licentiate Theses, ISSN 1651-9256 ; 144
Keyword
annual performance, combined heat and power, drying, ethanol, integration, part-load., årliga prestation, kraftvärme, torkning, etanol, integration, del-last.
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-13185 (URN)978-91-7485-045-1 (ISBN)
Presentation
2011-11-28, Kappa, Mälardalen University, Västerås, 13:30 (English)
Opponent
Supervisors
Projects
REMOWE, CSC
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2011-11-09Bibliographically approved
2. Regional Energy Systems with Retrofitted Combined Heat and Power (CHP) Plants
Open this publication in new window or tab >>Regional Energy Systems with Retrofitted Combined Heat and Power (CHP) Plants
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fossil fuel depletion, economic development, urban expansion and climate change present tough challenges to municipal- and regional-scale energy systems. Regional energy system planning, including waste treatment, renewable energy supply, energy efficiency, and climate change, are considered essential to meet these challenges and move toward a sustainable society. This thesis includes studies on energy system from municipal waste, potential for a fossil fuel-independent regional energy system with increased renewable energy products using waste as one of energy sources, and the performance of biomass-fired combined heat and power (CHP) plants. A top-down method is adopted to organize the studies, from national waste-to-energy (WtE) scenarios to individual energy plants.

The first study considers the overall potential contribution of WtE to energy supply and greenhouse gas (GHG) emissions mitigation in Sweden until 2050 under several different scenarios. Depending on WtE scenario considered, the study shows that WtE can supply energy between 38 and 186 TWh and mitigate between CO2 of 1 and 12 Mt per year by 2050 based on the baseline of year 2010.

At a regional level, static and dynamic optimization models with a focus on WtE are developed for two regions in Sweden and Finland. The former is used to investigate the possibilities of optimal positioning of new energy plants, retrofitting existing energy plants and planting energy crops. The latter case study is on regional heat and power production using biogas generated from agricultural and livestock wastes. Centralized biogas production units perform better than distributed production regarding energy and carbon balance though the net energy output is negligible. However, a significant GHG emission can be reduced compared to the present status.

Retrofitting existing conventional CHP plants is another option for improving regional energy system. The study shows that integrating heat-demanded processes such as drying, bioethanol and pellet production with existing CHP plants can improve overall energy efficiency and power output, increase annual operation time and reduce production cost as well as mitigate GHG emissions.

 It is recommended that building new WtE/energy plants at optimum sites, upgrading the existing energy plants, expanding the agricultural/forestry waste/residues output (biomass) and planting more energy crops shall be taken into considerations for the future regional energy systems.

Abstract [sv]

Utarmning av fossila bränslekällor, ekonomisk utveckling, städernas utbredning och klimatförändring är svåra utmaningar för kommunala- och regionala energisystem. Planering av det regionala energisystemet, inklusive avfallshantering, förnyelsebara energikällor, energieffektivisering och hänsyn till klimatförändringar, anses avgörande för att möta dessa utmaningar och gå mot ett hållbart samhälle. Denna avhandling innehåller studier av energisystem centrerad kring hushållsavfall, potentialet för fossilbränslefria regionala energisystem som utnyttjar ökad andel förnyelsebara energiprodukter med avfall som en energikälla och prestandautvärdering av ett biomassa-eldat kraftvärmeverk. Studierna har organiserats efter storlek på system, från nationella avfall-till-energi scenarier till enskilda kraftverk.

 

Den första studien behandlar övergripande möjligheten att genom avfall-till-energi bidra till energiförsörjningen och begränsa utsläppet av växthusgaser i Sverige till 2050 under flera olika scenarier. Beroendet på avfall-till-energiscenario visar studien att genom att utnyttja avfall kan mellan 38 och 186 TWh energi levereras och dessutom kan koldioxidutsläppen reduceras med 1-12 miljoner ton till år 2050 med 2010 som basår.

 

På den regionala nivån, statiska och dynamiska optimeringsmodeller, med fokus på avfall-till-energi, är utvecklats för två regioner, en i Sverige och en i Finland. Det första modellen används för hitta den optimala placeringen av nya energianläggningar, anpassning av befintliga anläggningar och placering av odlingar av energigrödor. Den senare ingår i en fallstudie av den regionala kraft- och värmeproduktionen genom utnyttjande av biogas producerad från jordbruksavfall och djurgödsel. Centraliserade biogasanläggningar presterar bättre än decentraliserad anläggningar när det gäller energi – och kolbalanser även om i båda fallen så är skillnaden mellan konsumerad mängd bränsle, värme och el och producerad värme och el försumbar. Däremot kan en betydande mängd av växthusgasutsläppet i båda fallen undvikas jämfört med nuläget.

 

Anpassning av befintliga konventionella kraftvärmeverk är ett annat alternativ för att förbättra det regionala energisystemet. Studien visar att genom att integrera värmekrävande processer såsom torkning, bioetanol- och pelletsproduktion med befintliga kraftvärmeverk kan den totala energieffektiviten och uteffekten förbättras, öka den årliga drifftiden och minska produktionskostnaderna och utsläppen av växthusgaser.

 

Rekommendationen är att för de framtida regionala energisystemen överväga att bygga nya avfall-till-energianläggningar med optimal placering, uppgradera befintliga energianläggningar utöka insamlandet av avfall/restprodukter från jord- och skogbruk och plantera mer energigrödor.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2012. 66 p.
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 132
Keyword
Combined heat and power, Waste-to-Energy (WtE), Regional energy system, Greenhouse gases (GHG), Retrofitting, Optimization, Kraftvärme, Avfall-till-Energi, Regionala Energisystem, Växthusgaser, Uppgradering, Optimering.
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-15966 (URN)978-91-7485-085-7 (ISBN)
Public defence
2012-12-10, Milos, Hogskolenplan 1, Vasteras, 13:30 (English)
Opponent
Supervisors
Available from: 2012-10-31 Created: 2012-10-29 Last updated: 2012-11-15Bibliographically approved

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